People are generally aware of the most common causes of hallucinations, like schizophrenia and a really high fever. But lesser known are the more rare causes; here are six you probably haven't heard about.

Migraines: Headaches That Don't Hurt Your Brain

Migraines currently affect about one in five women and while these headaches are common, there are still many unanswered questions surrounding this complex condition.

Migraines have been linked to an increased risk of stroke and structural brain lesions, but it has remained unclear as to whether migraines had other negative consequences associated with dementia or cognitive decline.

However, after analyzing data from 6,349 women aged 65 or older who participated in the Women’s Health Study researchers from Brigham and Women's Hospital in Boston found that migraines are not associated with cognitive decline, according to a study published in the British Medical Journal.

"Previous studies on migraines and cognitive decline were small and unable to identify a link between the two. Our study was large enough to draw the conclusion that migraines, while painful, are not strongly linked to cognitive decline," explained lead author Pamela Rist, a research fellow in the Division of Preventive Medicine at BWH, said in a news release.

Participants in the study had provided information about their migraine status and participated in cognitive testing during follow-up.

The participants were classified into four groups based on migraine status at baseline: no history of migraine, migraine with aura (transient neurology symptoms mostly of the visual field), migraine without aura and past history of migraine.

Researcher conducted cognitive testing in two year intervals up to three times.

"Compared with women with no history of migraine, those who experienced migraine with or without aura did not have significantly different rates of cognitive decline," explained Rist. "This is an important finding for both physicians and patients. Patients with migraine and their treating doctors should be reassured that migraine may not have long term consequences on cognitive function."

However, researchers did find some effect modification by age for those with a past history of migraine, suggesting that older women had faster rates of cognitive decline than younger women.

Rist and her team also found that women who suffered migraine with aura or those who've experienced a cardiovascular event had faster rates of decline on the category fluency test than those without a cardiovascular event, suggesting that executive cognitive function is especially affected by clinical or subclinical stroke.

While there is still a lot of mystery surrounding the effects of migraines, researchers say that the latest findings offer promising evidence for patients and doctors.

However, they noted that more research needs to be done to understand the consequences of migraine on the brain and to establish ways to influence the disease for more effective treatment strategies.